Slow 3G is almost always local to a cell. It may be on either side of the cell, wired or wireless. It is usually a function of load. Move to a different cell.

If the cell is your home cell, you should prefer WiFi and you may wish to consider a microcell.

Note that I said "almost always." The exceptional case is local to the device. Compare to another phone in the same location. Note that radios do not usually fail this way. Most failure modes are binary; the device works or it does not. Rarely does it fail by slowing down. In any case, if the problem persists across cells, take it back to Apple. Actually, this is a good case, the only one that you can do much about.

Finally, while the AT&T service level is improving, there are still a few communities, e.g., NYC and SF, where AT&T service is generally bad. If you are in one of these, your neighbors will all see similar service. In fairness to AT&T, most of these situations are the result of local political situations, e.g., NIMBY, corruption.